Significant efforts have been devoted to the development of miniaturized mechanical devices and particularly to devices that are well suited to be integrated with semiconductor electronic components. Processing techniques similar to those used in integrated circuit manufacturing may be utilized to produce miniaturized mechanical components which have a wide variety of practical applications, including pressure sensors and other types of sensors, micromechanical electrical switches, resonators and filters, and on-chip mass spectrometers, among many other applications. Such microminiaturized mechanical and electrical devices are commonly referred to as microelectromechanical systems (MEMS). As improvements in manufacturing technology have allowed the continual reduction in size of electronic semiconductor components, micromechanical devices have similarly been developed with progressively smaller feature sizes. Electromechanical devices which have feature sizes less than a micrometer and down to a few nanometers are sometimes referred to as nanoelectromechanical systems (NEMS).
In the manufacturing of MEMS and NEMS devices, a typical step in the process involves the deposition or formation of a patterned structure on a sacrificial layer, followed by wet etching of the sacrificial layer to free the mechanical structure and allow it to be suspended as a bridge or cantilever. As the cross-sectional size of these suspended structures is reduced, particularly into the range of a fraction of a micrometer, serious problems are encountered which significantly reduce the yield of good devices that are obtained after the processing is completed. A primary problem is that the wet etchants used to etch out the sacrificial layer beneath the desired structure may attack and partially dissolve the material of the desired structure. For example, for silicon structures formed on a silicon dioxide sacrificial layer, the wet etchants used to dissolve the sacrificial layer will, to some degree, also attack and dissolve the silicon. The amount of material removed generally is of little or no consequence with respect to suspended structures having dimensions in the range of several hundred or several thousand nanometers. However, where the suspended structures have very small cross-sectional dimensions (height or width or both) in the range of a few hundred nanometers or less, the wet etchant can attack and damage a significant portion of the material of the silicon suspended structure during the time required to completely etch away the silicon dioxide sacrificial layer. Another problem encountered with very fine featured suspended structures is that the structures may collapse or sag during the production process as the wet etchant is being removed, possibly causing permanent bending of the suspended structure, or even adhesion of the suspended structure to the underlying substrate if it touches the substrate. The net result is that the yield (the proportion of good devices compared to useless devices formed during processing) drastically decreases as the feature size of the micromechanical structures decreases.